Negative-parity yrast states inGd150

High-spin states populated by the ${}_{}{}^{150}{}_{}{}^{}\mathrm{Sm}(\alpha ,4n){}_{}{}^{150}{}_{}{}^{}\mathrm{Gd}$ reaction have been studied by in-beam $\gamma$-ray and conversion-electron spectroscopy. Conversion-electron data for the decay of 5.8-min ${}_{}{}^{150}{}_{}{}^{}\mathrm{Tb}$ to levels in ${}_{}{}^{150}{}_{}{}^{}\mathrm{Gd}$ have also been obtained. The proposed level scheme for ${}_{}{}^{150}{}_{}{}^{}\mathrm{Gd}$ includes 21 levels, 11 of which are previously unreported. A sequence of odd-spin negative-parity states from ${17}^{-}$ to $3^{-}$ carries most of the yrast-cascade intensity. This sequence is interpreted as containing two quasirotational bands. The states below ${11}^{-}$ represent a band built on an octupole vibration while those above ${11}^{-}$ constitute a band built on an $\nu \left(i_{\frac{13}{2}}{h}_{\frac{9}{2}}\right){11}^{-}$, quasiparticle state. Other quasiparticle states arising from the $\nu \left(i_{\frac{13}{2}}{h}_{\frac{9}{2}}\right)$ and $\nu \left(f_{\frac{7}{2}}{h}_{\frac{9}{2}}\right)$ configurations are proposed.